Re: [Qemu-devel] [PATCHv2 2/8] spapr: Remove 'awaiting_allocation' DRC flag

[Laurent Vivier <lvivier@redhat.com>]

On 12/07/2017 07:53, David Gibson wrote:
> The awaiting_allocation flag in the DRC was introduced by aab9913
> "spapr_drc: Prevent detach racing against attach for CPU DR", allegedly to
> prevent a guest crash on racing attach and detach.  Except.. information
> from the BZ actually suggests a qemu crash, not a guest crash.  And there
> shouldn't be a problem here anyway: if the guest has already moved the DRC
> away from UNUSABLE state, the detach would already be deferred, and if it
> hadn't it should be safe to detach it (the guest should fail gracefully
> when it attempts to change the allocation state).
> 
> I think this was probably just a bandaid for some other problem in the
> state management.  So, remove awaiting_allocation and associated code.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Reviewed-by: Laurent Vivier <lvivier@redhat.com>

> ---
>  hw/ppc/spapr_drc.c         | 25 +++----------------------
>  include/hw/ppc/spapr_drc.h |  1 -
>  2 files changed, 3 insertions(+), 23 deletions(-)
> 
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index 9b07f80..89ba3d6 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -170,19 +170,13 @@ static uint32_t drc_set_usable(sPAPRDRConnector *drc)
>      if (!drc->dev) {
>          return RTAS_OUT_NO_SUCH_INDICATOR;
>      }
> -    if (drc->awaiting_release && drc->awaiting_allocation) {
> -        /* kernel is acknowledging a previous hotplug event
> -         * while we are already removing it.
> -         * it's safe to ignore awaiting_allocation here since we know the
> -         * situation is predicated on the guest either already having done
> -         * so (boot-time hotplug), or never being able to acquire in the
> -         * first place (hotplug followed by immediate unplug).
> -         */
> +    if (drc->awaiting_release) {
> +        /* Don't allow the guest to move a device away from UNUSABLE
> +         * state when we want to unplug it */
>          return RTAS_OUT_NO_SUCH_INDICATOR;
>      }
>  
>      drc->allocation_state = SPAPR_DR_ALLOCATION_STATE_USABLE;
> -    drc->awaiting_allocation = false;
>  
>      return RTAS_OUT_SUCCESS;
>  }
> @@ -357,10 +351,6 @@ void spapr_drc_attach(sPAPRDRConnector *drc, DeviceState *d, void *fdt,
>      drc->fdt = fdt;
>      drc->fdt_start_offset = fdt_start_offset;
>  
> -    if (spapr_drc_type(drc) != SPAPR_DR_CONNECTOR_TYPE_PCI) {
> -        drc->awaiting_allocation = true;
> -    }
> -
>      object_property_add_link(OBJECT(drc), "device",
>                               object_get_typename(OBJECT(drc->dev)),
>                               (Object **)(&drc->dev),
> @@ -398,12 +388,6 @@ void spapr_drc_detach(sPAPRDRConnector *drc, DeviceState *d, Error **errp)
>          return;
>      }
>  
> -    if (drc->awaiting_allocation) {
> -        drc->awaiting_release = true;
> -        trace_spapr_drc_awaiting_allocation(spapr_drc_index(drc));
> -        return;
> -    }
> -
>      spapr_drc_release(drc);
>  }
>  
> @@ -426,8 +410,6 @@ void spapr_drc_reset(sPAPRDRConnector *drc)
>          spapr_drc_release(drc);
>      }
>  
> -    drc->awaiting_allocation = false;
> -
>      if (drc->dev) {
>          /* A device present at reset is coldplugged */
>          drc->isolation_state = SPAPR_DR_ISOLATION_STATE_UNISOLATED;
> @@ -493,7 +475,6 @@ static const VMStateDescription vmstate_spapr_drc = {
>          VMSTATE_UINT32(dr_indicator, sPAPRDRConnector),
>          VMSTATE_BOOL(configured, sPAPRDRConnector),
>          VMSTATE_BOOL(awaiting_release, sPAPRDRConnector),
> -        VMSTATE_BOOL(awaiting_allocation, sPAPRDRConnector),
>          VMSTATE_END_OF_LIST()
>      }
>  };
> diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
> index 715016b..18a196e 100644
> --- a/include/hw/ppc/spapr_drc.h
> +++ b/include/hw/ppc/spapr_drc.h
> @@ -200,7 +200,6 @@ typedef struct sPAPRDRConnector {
>      sPAPRConfigureConnectorState *ccs;
>  
>      bool awaiting_release;
> -    bool awaiting_allocation;
>  
>      /* device pointer, via link property */
>      DeviceState *dev;
>